1. Field of the Invention
This invention relates generally to the art of maintaining networks of main and delivery high- and low-pressure steel pipelines, and more particularly concerns a method of forming a protective coating on the inner surface of pipelines and a device by means of which such a method can be carried out in a number of industrial applications.
The proposed method can be used for applying protective coatings to pipelines under construction and for making repairs of pipelines after extensive use.
2. Description of the Prior Art
At present, pipelines are protected against corrosion and old pipelines are put to new use by applying a protective coating to their inner surface.
Application of protective coatings to the inner surface of pipelines is carried out by a wide range of methods and devices.
There is known a method of applying a protective coating to the inner surface of pipelines which involves sticking a flexible hose (or shell) to the pipeline interior surface (c.f., e.g., Patent of Great Britain No. 2,082,285 Cl. F 2P 32).
This method envisages the formation of a coating by introducing a porous hose preliminarily impregnated with an adhesive to the pipeline interior. This porous hose is inserted into a flexible hose fabricated from a polymer material. The hoses with their ends turned inside out are then affixed to the inner wall of the pipeline so that the porous hose is placed between the pipeline wall and the polymer hose. By feeding water to a cavity formed by the portion of the hoses turned inside out the latter are moved lengthwise of the pipeline and pressed against the pipeline inner surface. The water is heater to 95.degree. C. for a bond to be formed between the hoses and the pipeline inner surface.
However, the above method of forming a protective coating is inherently complicated and results in high expenditures associated with pipeline construction, since the application of such coatings necessitates preparation of hoses of which one should be impregnated and drawn through the other hose. The method also requires that water inside the pipeline should be heated for the thus formed coating to set. The use of two hoses complicates their application to the pipeline, whereas the weight of the two hoses puts limitations as to the length of coating application within one pass to 200 m, which in turn requires more time for forming a coating. In addition, thin-wall polymer hoses susceptible to rupture are not adaptable for use in the above method.